Friend of a friend? @johnpowell & @dappled_leaves make good points.
Still, here’s my attempt at “concise, smart, and maybe a little venomous”:
“Yes, I knew palindromes were a thing. And anagrams. But I had somehow deluded myself into thinking my fellow humans were intelligent, informed, compassionate, and self-aware. Thank you for reminding me there are still some horribly ignorant bigots trying to blame their own inadequacies and vexations on others. I somehow thought we were moving past this sort of crap. My mistake.”
You could also start posting links to articles, and writing your own posts, discussing the issues in intelligent ways—just “coincidentally.” Demonstrating just how ridiculous this friend-of-a-friend is without directly engaging him…